1. Field of the Invention
The invention resides in the field of guidewires for the insertion of catheters and other devices for the diagnosis and treatment of vascular disease.
Guidewires are small diameter devices which provide torsional, axial and radial rigidity and are utilized to insert catheters into the anatomy and to guide catheters into areas of vascular anatomy. Guidewires are generally constructed of materials such as stainless steel rod or tube stock and have a coiled metallic spring around their entirety or only at the distal end. The guidewire body, be it tube or rod, imparts torque and axial strength while the spring is soft to be atraumatic to the vascular tissue. Guidewires can vary in size of outer diameter from a few thousandths to 0.080 inches and are designated by diameter in thousandths of an inch. Steerable guidewires generally range in size of outer diameter from 0.010 inches to 0.020 inches.
Catheters are larger than guidewires and may be single or multiple lumen tubes of somewhat different construction and materials. They are designated by French size and vary from a few French to as large as 50 French for bypass surgery. One French equals 0.013 inches. Standard diagnostic catheters are generally made of a soft material such as plastic and are used for a variety of diagnostic and therapeutic applications. Diagnostic catheters are sometimes wire braid reinforced or of coaxial construction with the inner tube having more rigidity than the outer tube to provide some control to the catheter.
Steerable PTCA catheters vary from as small as 3 French to as large as 5 French. The smallest steerable catheter would be approximately 0.041 inches. Steerable catheters, unlike diagnostic catheters, do not generally have any reinforce-ment to provide torque characteristics. As such steerable catheters are guided into the vasculature and to the area of interest in the vasculature over steerable guidewires which provide torque and rigidity.
2. Description of the Prior Art
Prior to therapeutic catheters for the treatment of vascular disease, guidewires were used to straighten and safely guide diagnostic catheters into parts of the vascular system where radiopaque dyes were injected to illuminate the vasculature under fluoroscopy for studying the anatomy prior to therapy. With the advent of balloon and laser catheters for unblocking obstructions in small diameter vessels, such as the coronary arteries, came the development of highly steerable guidewires of small diameter for accessing these lesions. The necessity for highly steerable guidewire devices came as a result of the tortuous pathways encountered in the coronary vasculature. These steerable guidewires additionally were designed with very soft atraumatic tips to avoid injury to the vasculature. Typically for a balloon dilatation procedure, a small diameter steerable guidewire is placed within a small diameter multiple lumen balloon catheter and the two advanced into the vasculature through a larger diameter guide catheter which has been placed from a remote vascular entry point. The guide catheter is similar to diagnostic angiographic catheters and is placed over a large diameter guidewire which straightens the guide catheter for entry into a remote area of the vasculature and facilitates manipulation of the catheter. At this point the large diameter guidewire is removed and the preformed tip of the guide catheter enables the catheter which has some torque capability to be positioned at the site of entry of the therapeutic catheter into the particular area of the vasculature. The guide catheter, unlike a diagnostic catheter, is stiffer and designed with the added support capability to facilitate advancement of the steerable guidewire and balloon catheter assembly into the remote narrow vasculature. The guide catheter for coronary dilatation procedures would be advanced to the coronary ostium. From this point the dilatation catheter and steerable guidewire assembly, which have been advanced through the guide catheter as an assembly, would exit from the guide catheter into the coronary vasculature. The steerable guidewire would be advanced several centimeters out the tip of the balloon catheter. Because of the atraumatic tip and torque characteristics the steerable guidewire would be used to access the area of obstruction. The balloon catheter would then be advanced over the steerable guidewire across the lesion. The balloon on the catheter would then be inflated to accomplish the therapy. However, the steerable guidewire therefore would merely support the balloon catheter in reaching and crossing the lesion. With many steerable systems pressure could be measured from the tip of the balloon catheter in conjunction with a pressure from the guide catheter to provide a gradient. The amount of gradient pre and post dilatation could be used as a measure of success. With these steerable systems, the therapeutic catheter could then be pulled back on the steerable guidewire out of the narrowing to study the results by dye injection. The steerable guidewire remains across the lesion in order to re-cross the lesion if necessary for additional therapy or should there be closure of the vessel in order to re-open the vessel. Alternatively, the therapeutic catheter can remain across the lesion and the steerable guidewire removed to be exchanged for another steerable guidewire of varying characteristics should this be deemed necessary.
The use of these systems is well known and a variety of systems comprising various steerable guidewires and various balloon catheters in combination has been developed. The variety of steerable guidewires and catheters for facilitating the procedure is extensive.
For example, in the area of guidewires, U.S. Pat. Nos. 4,545,390, Leary, and 3,789,841, Antoshkiw, both show distal tips formed of helically wound springs surrounding fixed tapered cores. U.S. Pat. No. 3,631,848, Muller, describes an axially movable distal tip extension tube of relatively short length.
A coil tip with tapered face edges which will curve toward the taper when pulled upon by an internal control wire is disclosed in U.S. Pat. Nos. 3,452,740, and 3,452,742, both to Muller. U.S. Pat. No. 4,650,467, Bonello shows a similar arrangement for inclining the tip by retraction of a control wire affixed thereto.
Additionally, U.S. Pat. No. 3,528,406, Jeckel et al. teaches the use of a fixed core wire having a reduced diameter in the spring tip portion of the wire. U.S. Pat. No. 3,625,200, Muller, discloses a curvable tip comprising solid cylindrical links engaging each other with ball and socket joints each of which is manipulatable by a fine core wire. Finally, U.S. Pat. No. 4,573,470, Samson shows a curved tip which is rotated in its entirety by rotating a core wire at the control handle.
The aforementioned guidewire designs and improvements were limited to providing additional control characteristics to steerable guidewires to facilitate catheter placement.
In the area of balloon catheters for dilatation or compression of plaque, U.S. Pat. 4,323,071 discloses such a catheter in which two concentric tubes are employed, the inner tube adapted to fit over a separate steerable guidewire. The distal end of the outer tube is sealed to contain the fluid. Visualization of the anatomy by fluoroscopy may be accomplished ahead of the catheter and guidewire by infusion of dye through the central tube around the steerable guidewire and out the distal tip of the catheter.
An alternative system is described in U.S. Pat. No. 4,582,181, Samson et al. in which a balloon is similarly formed in a catheter outer tube having a separate guidewire extending therethrough and inflation fluid is delivered through a tube disposed side by side with the guidewire. In this system the guidewire is moveable within the catheter axially but the distal end is larger than the catheter tube through which it passes and as such may not be removed for guidewire exchange or may not be left in place while the catheter is removed for catheter exchange as is typical in standard steerable catheter and guidewire systems. Fluid may be infused in this system around the guidewire and out the distal tip of the catheter for dye tracing. The smaller wire permits a lower profile catheter system but obviates wire exchange.
Finally in U.S. Pat. No. 4,573,470, Samson et al. describes a Low-Profile Steerable Intraoperative Balloon Dilatation Catheter system wherein the catheter and the guidewire are bonded together to form a liquid-tight seal at the distal end of the catheter. The guidewire and balloon are manipulated as a unit with the guidewire fixed relative to the catheter to prohibit axial movement of the guidewire within the balloon catheter but enabling the guidewire to provide torque to the balloon catheter as an integral unit. In this system fluid is contained solely within the catheter.
The progression of developments in the area of steerable guidewire/catheter systems has enabled the access of smaller more tortuous vessels through the reduction of the overall outside diameter (profile) of the catheter/guidewire systems. In doing so the ability to provide distal dye injections, catheter exchanges and guidewire exchanges has been lost in some of these designs.